/*

 * Copyright (c) 2001, 2019, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 *

 */

#include "precompiled.hpp"

#include "gc/shared/gcId.hpp"

#include "gc/shared/workgroup.hpp"

#include "gc/shared/workerManager.hpp"

#include "memory/allocation.hpp"

#include "memory/allocation.inline.hpp"

#include "runtime/atomic.hpp"

#include "runtime/os.hpp"

#include "runtime/semaphore.hpp"

#include "runtime/thread.inline.hpp"

// Definitions of WorkGang methods.

// The current implementation will exit if the allocation

// of any worker fails.

void  AbstractWorkGang::initialize_workers() {

  log_develop_trace(gc, workgang)("Constructing work gang %s with %u threads", name(), total_workers());

  _workers = NEW_C_HEAP_ARRAY(AbstractGangWorker*, total_workers(), mtInternal);

  add_workers(true);

}

AbstractGangWorker* AbstractWorkGang::install_worker(uint worker_id) {

  AbstractGangWorker* new_worker = allocate_worker(worker_id);

  set_thread(worker_id, new_worker);

  return new_worker;

}

void AbstractWorkGang::add_workers(bool initializing) {

  add_workers(_active_workers, initializing);

}

void AbstractWorkGang::add_workers(uint active_workers, bool initializing) {

  os::ThreadType worker_type;

  if (are_ConcurrentGC_threads()) {

    worker_type = os::cgc_thread;

  } else {

    worker_type = os::pgc_thread;

  }

  uint previous_created_workers = _created_workers;

  _created_workers = WorkerManager::add_workers(this,

                                                active_workers,

                                                _total_workers,

                                                _created_workers,

                                                worker_type,

                                                initializing);

  _active_workers = MIN2(_created_workers, _active_workers);

  WorkerManager::log_worker_creation(this, previous_created_workers, _active_workers, _created_workers, initializing);

}

AbstractGangWorker* AbstractWorkGang::worker(uint i) const {

  // Array index bounds checking.

  AbstractGangWorker* result = NULL;

  assert(_workers != NULL, "No workers for indexing");

  assert(i < total_workers(), "Worker index out of bounds");

  result = _workers[i];

  assert(result != NULL, "Indexing to null worker");

  return result;

}

void AbstractWorkGang::print_worker_threads_on(outputStream* st) const {

  uint workers = created_workers();

  for (uint i = 0; i < workers; i++) {

    worker(i)->print_on(st);

    st->cr();

  }

}

void AbstractWorkGang::threads_do(ThreadClosure* tc) const {

  assert(tc != NULL, "Null ThreadClosure");

  uint workers = created_workers();

  for (uint i = 0; i < workers; i++) {

    tc->do_thread(worker(i));

  }

}

// WorkGang dispatcher implemented with semaphores.

//

// Semaphores don't require the worker threads to re-claim the lock when they wake up.

// This helps lowering the latency when starting and stopping the worker threads.

class SemaphoreGangTaskDispatcher : public GangTaskDispatcher {

  // The task currently being dispatched to the GangWorkers.

  AbstractGangTask* _task;

  volatile uint _started;

  volatile uint _not_finished;

  // Semaphore used to start the GangWorkers.

  Semaphore* _start_semaphore;

  // Semaphore used to notify the coordinator that all workers are done.

  Semaphore* _end_semaphore;

public:

  SemaphoreGangTaskDispatcher() :

      _task(NULL),

      _started(0),

      _not_finished(0),

      _start_semaphore(new Semaphore()),

      _end_semaphore(new Semaphore())

{ }

  ~SemaphoreGangTaskDispatcher() {

    delete _start_semaphore;

    delete _end_semaphore;

  }

  void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers) {

    // No workers are allowed to read the state variables until they have been signaled.

    _task         = task;

    _not_finished = num_workers;

    // Dispatch 'num_workers' number of tasks.

    _start_semaphore->signal(num_workers);

    // Wait for the last worker to signal the coordinator.

    _end_semaphore->wait();

    // No workers are allowed to read the state variables after the coordinator has been signaled.

    assert(_not_finished == 0, "%d not finished workers?", _not_finished);

    _task    = NULL;

    _started = 0;

  }

  WorkData worker_wait_for_task() {

    // Wait for the coordinator to dispatch a task.

    _start_semaphore->wait();

    uint num_started = Atomic::add(1u, &_started);

    // Subtract one to get a zero-indexed worker id.

    uint worker_id = num_started - 1;

    return WorkData(_task, worker_id);

  }

  void worker_done_with_task() {

    // Mark that the worker is done with the task.

    // The worker is not allowed to read the state variables after this line.

    uint not_finished = Atomic::sub(1u, &_not_finished);

    // The last worker signals to the coordinator that all work is completed.

    if (not_finished == 0) {

      _end_semaphore->signal();

    }

  }

};

class MutexGangTaskDispatcher : public GangTaskDispatcher {

  AbstractGangTask* _task;

  volatile uint _started;

  volatile uint _finished;

  volatile uint _num_workers;

  Monitor* _monitor;

 public:

  MutexGangTaskDispatcher() :

    _task(NULL),

    _started(0),

    _finished(0),

    _num_workers(0),

    _monitor(new Monitor(Monitor::leaf, "WorkGang dispatcher lock", false, Monitor::_safepoint_check_never)) {

  }

  ~MutexGangTaskDispatcher() {

    delete _monitor;

  }

  void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers) {

    MonitorLocker ml(_monitor, Mutex::_no_safepoint_check_flag);

    _task        = task;

    _num_workers = num_workers;

    // Tell the workers to get to work.

    _monitor->notify_all();

    // Wait for them to finish.

    while (_finished < _num_workers) {

      ml.wait();

    }

    _task        = NULL;

    _num_workers = 0;

    _started     = 0;

    _finished    = 0;

  }

  WorkData worker_wait_for_task() {

    MonitorLocker ml(_monitor, Mutex::_no_safepoint_check_flag);

    while (_num_workers == 0 || _started == _num_workers) {

      _monitor->wait();

    }

    _started++;

    // Subtract one to get a zero-indexed worker id.

    uint worker_id = _started - 1;

    return WorkData(_task, worker_id);

  }

  void worker_done_with_task() {

    MonitorLocker ml(_monitor, Mutex::_no_safepoint_check_flag);

    _finished++;

    if (_finished == _num_workers) {

      // This will wake up all workers and not only the coordinator.

      _monitor->notify_all();

    }

  }

};

static GangTaskDispatcher* create_dispatcher() {

  if (UseSemaphoreGCThreadsSynchronization) {

    return new SemaphoreGangTaskDispatcher();

  }

  return new MutexGangTaskDispatcher();

}

WorkGang::WorkGang(const char* name,

                   uint  workers,

                   bool  are_GC_task_threads,

                   bool  are_ConcurrentGC_threads) :

    AbstractWorkGang(name, workers, are_GC_task_threads, are_ConcurrentGC_threads),

    _dispatcher(create_dispatcher())

{ }

WorkGang::~WorkGang() {

  delete _dispatcher;

}

AbstractGangWorker* WorkGang::allocate_worker(uint worker_id) {

  return new GangWorker(this, worker_id);

}

void WorkGang::run_task(AbstractGangTask* task) {

  run_task(task, active_workers());

}

void WorkGang::run_task(AbstractGangTask* task, uint num_workers) {

  guarantee(num_workers <= total_workers(),

            "Trying to execute task %s with %u workers which is more than the amount of total workers %u.",

            task->name(), num_workers, total_workers());

  guarantee(num_workers > 0, "Trying to execute task %s with zero workers", task->name());

  uint old_num_workers = _active_workers;

  update_active_workers(num_workers);

  _dispatcher->coordinator_execute_on_workers(task, num_workers);

  update_active_workers(old_num_workers);

}

AbstractGangWorker::AbstractGangWorker(AbstractWorkGang* gang, uint id) {

  _gang = gang;

  set_id(id);

  set_name("%s#%d", gang->name(), id);

}

void AbstractGangWorker::run() {

  initialize();

  loop();

}

void AbstractGangWorker::initialize() {

  assert(_gang != NULL, "No gang to run in");

  os::set_priority(this, NearMaxPriority);

  log_develop_trace(gc, workgang)("Running gang worker for gang %s id %u", gang()->name(), id());

  assert(!Thread::current()->is_VM_thread(), "VM thread should not be part"

         " of a work gang");

}

bool AbstractGangWorker::is_GC_task_thread() const {

  return gang()->are_GC_task_threads();

}

bool AbstractGangWorker::is_ConcurrentGC_thread() const {

  return gang()->are_ConcurrentGC_threads();

}

void AbstractGangWorker::print_on(outputStream* st) const {

  st->print("\"%s\" ", name());

  Thread::print_on(st);

  st->cr();

}

void AbstractGangWorker::print() const { print_on(tty); }

WorkData GangWorker::wait_for_task() {

  return gang()->dispatcher()->worker_wait_for_task();

}

void GangWorker::signal_task_done() {

  gang()->dispatcher()->worker_done_with_task();

}

void GangWorker::run_task(WorkData data) {

  GCIdMark gc_id_mark(data._task->gc_id());

  log_develop_trace(gc, workgang)("Running work gang: %s task: %s worker: %u", name(), data._task->name(), data._worker_id);

  data._task->work(data._worker_id);

  log_develop_trace(gc, workgang)("Finished work gang: %s task: %s worker: %u thread: " PTR_FORMAT,

                                  name(), data._task->name(), data._worker_id, p2i(Thread::current()));

}

void GangWorker::loop() {

  while (true) {

    WorkData data = wait_for_task();

    run_task(data);

    signal_task_done();

  }

}

// *** WorkGangBarrierSync

WorkGangBarrierSync::WorkGangBarrierSync()

  : _monitor(Mutex::safepoint, "work gang barrier sync", true,

             Monitor::_safepoint_check_never),

    _n_workers(0), _n_completed(0), _should_reset(false), _aborted(false) {

}

WorkGangBarrierSync::WorkGangBarrierSync(uint n_workers, const char* name)

  : _monitor(Mutex::safepoint, name, true, Monitor::_safepoint_check_never),

    _n_workers(n_workers), _n_completed(0), _should_reset(false), _aborted(false) {

}

void WorkGangBarrierSync::set_n_workers(uint n_workers) {

  _n_workers    = n_workers;

  _n_completed  = 0;

  _should_reset = false;

  _aborted      = false;

}

bool WorkGangBarrierSync::enter() {

  MonitorLocker ml(monitor(), Mutex::_no_safepoint_check_flag);

  if (should_reset()) {

    // The should_reset() was set and we are the first worker to enter

    // the sync barrier. We will zero the n_completed() count which

    // effectively resets the barrier.

    zero_completed();

    set_should_reset(false);

  }

  inc_completed();

  if (n_completed() == n_workers()) {

    // At this point we would like to reset the barrier to be ready in

    // case it is used again. However, we cannot set n_completed() to

    // 0, even after the notify_all(), given that some other workers

    // might still be waiting for n_completed() to become ==

    // n_workers(). So, if we set n_completed() to 0, those workers

    // will get stuck (as they will wake up, see that n_completed() !=

    // n_workers() and go back to sleep). Instead, we raise the

    // should_reset() flag and the barrier will be reset the first

    // time a worker enters it again.

    set_should_reset(true);

    ml.notify_all();

  } else {

    while (n_completed() != n_workers() && !aborted()) {

      ml.wait();

    }

  }

  return !aborted();

}

void WorkGangBarrierSync::abort() {

  MutexLocker x(monitor(), Mutex::_no_safepoint_check_flag);

  set_aborted();

  monitor()->notify_all();

}

// SubTasksDone functions.

SubTasksDone::SubTasksDone(uint n) :

  _tasks(NULL), _n_tasks(n), _threads_completed(0) {

  _tasks = NEW_C_HEAP_ARRAY(uint, n, mtInternal);

  clear();

}

bool SubTasksDone::valid() {

  return _tasks != NULL;

}

void SubTasksDone::clear() {

  for (uint i = 0; i < _n_tasks; i++) {

    _tasks[i] = 0;

  }

  _threads_completed = 0;

#ifdef ASSERT

  _claimed = 0;

#endif

}

bool SubTasksDone::try_claim_task(uint t) {

  assert(t < _n_tasks, "bad task id.");

  uint old = _tasks[t];

  if (old == 0) {

    old = Atomic::cmpxchg(1u, &_tasks[t], 0u);

  }

  bool res = old == 0;

#ifdef ASSERT

  if (res) {

    assert(_claimed < _n_tasks, "Too many tasks claimed; missing clear?");

    Atomic::inc(&_claimed);

  }

#endif

  return res;

}

void SubTasksDone::all_tasks_completed(uint n_threads) {

  uint observed = _threads_completed;

  uint old;

  do {

    old = observed;

    observed = Atomic::cmpxchg(old+1, &_threads_completed, old);

  } while (observed != old);

  // If this was the last thread checking in, clear the tasks.

  uint adjusted_thread_count = (n_threads == 0 ? 1 : n_threads);

  if (observed + 1 == adjusted_thread_count) {

    clear();

  }

}

SubTasksDone::~SubTasksDone() {

  FREE_C_HEAP_ARRAY(uint, _tasks);

}

// *** SequentialSubTasksDone

void SequentialSubTasksDone::clear() {

  _n_tasks   = _n_claimed   = 0;

  _n_threads = _n_completed = 0;

}

bool SequentialSubTasksDone::valid() {

  return _n_threads > 0;

}

bool SequentialSubTasksDone::try_claim_task(uint& t) {

  t = _n_claimed;

  while (t < _n_tasks) {

    uint res = Atomic::cmpxchg(t+1, &_n_claimed, t);

    if (res == t) {

      return true;

    }

    t = res;

  }

  return false;

}

bool SequentialSubTasksDone::all_tasks_completed() {

  uint complete = _n_completed;

  while (true) {

    uint res = Atomic::cmpxchg(complete+1, &_n_completed, complete);

    if (res == complete) {

      break;

    }

    complete = res;

  }

  if (complete+1 == _n_threads) {

    clear();